The Atmospheric Environment Problem in East Asia for the Twenty-first Century

Summary

Large amounts of air pollutants have recently been emitted from East Asian countries. The emission amount of anthropogenic sulfur in East Asia is especially enormous, estimated to be 30 million tons/year. This amount accounts for about 30% of the anthropogenic sulfur in the world. Most of the anthropogenic sulfur in the atmosphere is washed out by rain and then deposited on the land. However, part of the anthropogenic sulfur emitted from East Asia is transported to the sea near Japan by westerly winds. SO₂ emitted by burning fossil fuel is oxidized to H₂SO₄ in the atmosphere. On land, the oxidized H₂SO₄ in generally neutralized with NH₃, which is generated from the soil by microorganism activity. On the other hand, in the marine atmosphere, SO₂ transported from the land is oxidized to H₂SO₄, but H₂SO₄ is not neutralized because few NH₃ exists in the marine atmosphere. Therefore, H₂SO₄ still exists as a strong acid in the marine atmosphere without neutralization. Furthermore, the transported SO₂ reacts with sea salt particles, which are composed of sodium chloride, and hydrogen chloride as a strong acid is then released from sea salt particles. Thus, the SO₂ transported from East Asia causes increased acidification of the marine atmosphere near Japan. In this study, observations were carried out at several remote islands near Japan and on the routes of vessels over the ocean, from 1991 to 1999, to understand the transport process of anthropogenic sulfur from East Asia and its influence on the marine atmosphere over the sea near Japan.